go: add «1701. Average Waiting Time»

Signed-off-by: Matej Focko <me@mfocko.xyz>

go/average-waiting-time.go

@@ -0,0 +1,15 @@
+package main
+
+func averageWaitingTime(customers [][]int) float64 {
+	waitingTime := 0
+
+	idleAt := 0
+	for _, customer := range customers {
+		arrives, length := customer[0], customer[1]
+
+		idleAt = max(idleAt, arrives) + length
+		waitingTime += idleAt - arrives
+	}
+
+	return float64(waitingTime) / float64(len(customers))
+}